For example, in some of disc brakes in which a pair of lug pieces which are provided at side portions of a backing plate of a friction pad so as to project are guided movably in pad guide grooves which are formed individually in caliper support arms of a caliper bracket, a pad return spring may be disposed between the lug pieces and the caliper support arms so that the friction pad is biased towards an opposite side to a disc rotor when the brake is released.
Such pad return spring may include a retainer portion which is disposed on a torque bearing surface of the pad guide groove to guide the moving friction pad and a pad return portion which biases the friction pad towards the opposite side to the disc rotor when the brake is released by bringing an extending piece which extends from the retainer portion into abutment with the lug piece via a curved portion. The pad return portion may be formed by forming an elastic portion by bending back an elongated piece in the direction of the disc rotor from a side of the retainer portion which is opposite to the disc rotor, causing a distal end side of the elongated piece to extend further towards the disc rotor and inclining a distal end portion of the elongated piece while bending it back along the extending direction into a curved shape. A space portion may be defined between the lug piece of the friction pad and the pad guide groove to permit the operation of the pad return portion (for example, refer to JP-5242481-B).
With such exemplary vehicle disc brake, however, the configuration of the pad return spring becomes complex, leading to fears that the production costs are increased. Further, in the friction pad, when the brake is applied, due to braking torque generated by the friction contact of the friction pad with the disc rotor, a force attempting to depress the friction pad radially inwards of the disc rotor acts at a disc-rotor-exit side and a force attempting to lift the friction pad radially outwards of the disc rotor acts at a disc-rotor-entrance side, whereby the lug piece at the disc-rotor-exit side is pressed against a surface of the pad guide groove which faces a radially inner side of the disc rotor, and the lug piece at the disc-rotor-entrance side is pressed against a surface of the pad guide groove which faces a radially outer side of the disc rotor. This causes the lug pieces to be fixed in the pad guide grooves. However, there are fears that the lug pieces are prevented from being fixed in the pad guide grooves by means of the spring force of the pad return portion, resulting in fears that brake noise or squeal is generated.
Meanwhile, there may also be provided a vehicle disc brake in which caliper support arms are provided on a caliper bracket which is fixed to a vehicle body so as to extend therefrom and a pad return spring is disposed between the caliper support arms and side portions of backing plates of a pair of friction pads which are disposed so as to hold a disc rotor therebetween to bias the friction pads so as to move away from the disc rotor. This pad return spring may include a backing plate attaching portion which is attached to the side portion of the backing plate and a pad return portion which extends from the backing plate attaching portion and which is brought into abutment with the caliper support art at a distal end thereof to thereby bias the friction pad so as to move away from the disc rotor (for example, refer to JP-2000-220670-A).
In such exemplary vehicle disc brake, however, the biasing force of the pad return spring increases according to the displacement amount, and therefore, for example, in such a state that the wear of the friction pad develops to a state resulting just before the friction pad is fully worn up, the biasing force with which the friction pad is caused to move away from the disc rotor increases so greatly that the friction pad is caused to retreat greatly. This increases the distance between the friction pad and the disc rotor, resulting in fears that the braking or brake pedal operation feeling is affected badly.